Mechanical Themes: WBR desert society, with Mummify and Exiling creatures from graveyards as a cost. GU river society, with Cyclic growth ("Thallid" mechanic).

50 Word summary:
The path to the afterlife is getting harder to achieve. Instead of finding peace, the recently deceased are returning as undead husks of their former selves. Some blame the secularization of the river society, who forgo the gods for bountiful life on earth. Others blame the cultists who desecrate the dead.

Pharaoh's Cat 1W
Creature - Cat
Lifelink
Mummify (When this dies, return it to the battlefield with a mummified counter and no abilities. It's a zombie in addition to its other types.)
1/2

Mummify suffers from the same problem as Undying or Scavenge; creatures with those abilities must be given stats that make them look bad even though they are very powerful. The use of a drawback ability like defender on a mummify creature is a great idea, and it's a way that mummify creatures can be balanced. I felt that you could also combat that problem if you put in more abilities like flying or deathtouch that make you happy to play a creature with smaller stats. I put my thoughts on the mummify mechanic on the mechanics thread here.